The n-heterocyclic polynuclear aromatic compounds are significant components of occupational and environmental contaminants such as coal tar, coke oven effluents, coal and oil shale processing effluents, automobile exhaust, and tobacco smoke. Members of the n-heterocyclic compounds have been shown to be potent carcinogens in many species, including the rat. Very little is known about the metabolism or mechanism of action of these carcinogens in mammalian systems because most of the previous metabolism studies have focused on the polycyclic aromatic hydrocarbon analogs, such as benzo(a)pyrene. The objective of this proposal is to investigate the metabolism and the pathways of metabolic activation of the model n-heterocyclic compound 7H-Dibenzo(c,g)carbazole(DBC) in a whole cell system of rat liver cell cultures. Identification of major metabolites will be accomplished by chemical analyses of DBC metabolism products isolated from rat liver cell culture media and by comparison of the products to standards obtained by chemical synthesis. Proposals for the pathways of activation will be generated by determining the mutagenic potential of the major metabolites in a whole cell system, testing the hypothesis that the nitrogen atom in the ring is involved in the metabolism of DBC leading to interaction with genetic material. A system for measuring unscheduled DNA synthesis in rat liver cell cultures will also be developed and used to test the hypothesis. In order to determine the role of n-heterocyclic polynuclear aromatics in occupational and environmental cancer, knowledge of the metabolism and disposition of the compounds in mammalian systems is necessary. The rat liver cell culture system is an ideal model for investigations of the metabolism, mutagenicity, and genotoxicity of this class of compounds. These studies will lead directly to hypotheses of the pathways of activation for DBC specifically and the n-heterocyclic compounds in general.